The Naming of Cats is a difficult matter,
It isn't just one of your holiday games;
You may think at first I'm as mad as a hatter
When I tell you, a cat must have THREE DIFFERENT NAMES.-T. S. Eliot
To use the workstation, you must first login. To do so, you must have (at the minimum) a login name by which the computer and other users will know you as well as a password which you should keep to yourself. In fact, since the password protects your work and the entire system from unauthorized and careless users, and since it is relatively easy for other users (all throughout the networked world no less!) to move through Unix systems, you should carefully guard your password.
In addition to your login name, the system will also assign you a user ID number and a group ID number. The user ID is a number which has a unique correspondence to your login name and which the system uses to keep tabs on you. When personal information is printed, such as in response to ls -l or ps commands, the system matches the user ID to the login name and prints out the login name. The group ID is a higher level identification shared among users which automatically permits (or forbids) a number of users permission to read and write the same files.
Essentially all Unix commands require you to end or activate them by hitting the key labeled Enter (or Return or Carriage return or [ret]). If you make a mistake keying in your command, you can correct it with the Backspace key if you have not yet entered in [ret]. You can often abort the running command with control-c, ctrl-c or ^ c or [Del].
After you have given the computer your login name and password, there is a short delay while the computer validates your account. It then responds by introducing itself, telling you if you have mail, possibly asking you to identify the type of terminal you are on, and setting off a chain of actions as commanded by a file labeled .login or .profile (see Appendix 6, Sample Dot Files). Finally, with a typically verbose Unix response, the computer presents you with a prompt as its way of saying, ``my wish is your command.''
The prompt you see depends upon the Unix shell you are using. By ``shell,'' we mean that part of Unix which interprets the user's commands. The three standard choices are the Borne shell, with program name sh; the C shell called csh; and the Korn shell, called ksh. The Borne shell came from System V and has fewer features than the others. BSD added the csh with useful features such as job control, the ability to reenter and edit past commands, and the ability to define your own commands via alias. The Korn shell is a newer offering from AT& which extends the Borne shell and adds many of the features of the C shell.
If the prompt % appears, it means you are using (or in) the C shell, csh. If the prompt $ appears, it means you are using the Borne or Korn shell. The # prompt is usually reserved for use by the all-knowing, all-powerful, system administrator, known as superuser or root. If you see it appear on your terminal and you are not acting as the system administrator, you should exit or logout before serious harm is done (seriously).
If a more personal and revealing prompt appears (like your name or your computer's name), it means the .cshrc (for csh) or .profile (for ksh or sh) file has been so set. You can select your shell by using the change shell commands csh, sh or ksh.